Full‐Scale Removal of DNAPL Constituents Using Steam‐Enhanced Extraction and Electrical Resistance Heating

Abstract

In 2003, the United States Department of Energy completed a full‐scale non–aqueous phase liquid (NAPL) remediation of Area A of the Northeast Site at the Young‐Rainey STAR Center, Largo, Florida. Area A covered an area of 930 m2 (10,000 square feet) and extended to a depth of 10.7 m (35 feet), representing a total cleanup volume of 9930 m3 (12,960 cubic yards). The site was contaminated with ∼2500 kg (5500 lb) of NAPL constituents such as trichloroethylene, cis‐1,2‐dichloroethylene, methylene chloride, toluene, and petroleum hydrocarbons. The site consists of a fine‐grained sand aquifer underlain by a Hawthorn clay at 9 m (30 feet) depth. The upper 1.5 m (5 feet) of this clay formed part of the remediation volume, as dense non–aqueous phase liquid was present in this layer. The site was remediated using a combination of steam‐enhanced extraction and electrical resistance heating. Operations lasted 4.5 months. The site was heated to the target temperatures within 6 weeks, at which time the mass removal rate increased more than 1000‐fold. After the target volume had been heated to or near boiling temperatures, pressure cycles were used to increase the mass removal rates, until a final phase of diminishing returns was reached. Postoperational sampling of soil and ground water at randomly selected locations showed the concentrations of all contaminants of concern (COC) to be well below the remedial goals. The majority of the ground water samples were below maximum contaminant level (MCL) for all the COC. The estimate of volatile organic contaminant (VOC) mass removed from the site (1130 kg = 2500 lb) agreed well with the estimate of VOC present before operation (1170 kg = 2580 lb). The postoperational sampling showed that ∼0.5 kg (1 pound) of VOCs remained in the remedial volume, and showed remedial efficiencies of between 99.85% and 99.99% for the four chemicals of concern. Since the postoperational sampling shows all concentrations to be below or close to ground water MCLs, the thermal remedy may be satisfactory for site closure without a polishing phase.

Steam-Enhanced Extraction Experiments, Simulations and Field Studies for Dense Non-Aqueous Phase Liquid Removal: A Review

“…The physical displacement is influenced by steam boiling point. Contaminants with low boiling point than water show greater recoveries [30][31][32][33][34]. The steam temperature, variable temperature and ambient temperature plays an important factor in the performance of SEE [14,18,35].…”

Combining steam injection with hydraulic fracturing for the in situ remediation of the unsaturated zone of a fractured soil polluted by jet fuel

“…During the last three decades, steam injection was tested as a method to remediate NAPLcontaminated sites (Hunt et al, 1988;Siegrist et al, 1998;Dablow et al, 2000;Kuhlman, 2002;Heron et al, 2005). In general, when steam is injected in a porous medium, three zones are developed: the steam zone, the variable temperature zone and the ambient temperature zone (Davis, 1998;.…”

Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

“…Although each of these mechanisms contributes to DNAPL removal, gas capture of vaporized VOCs is the dominant mechanism of removal during a thermal remediation application (e.g., Baker and Hiester, 2009;Beyke and Fleming, 2005;Heron et al, 2005Heron et al, , 2006Heron et al, , 2013Vermeulen and McGee, 2000). As such, the effectiveness of ISTT requires that temperatures are high enough within the treatment volume to vaporize VOCs and establish connected gas transport pathways to soil vapor or multiphase extraction points (e.g., Baker and Hiester, 2009;Heron et al, 2006;McGee et al, 2004).…”